The present invention relates to flame-retardant thermoplastic resin compositions and more particularly, relates to flame-retardant thermoplastic resin compositions having excellent mold releasability, heat stability and light resistance.
Flame-retardant ABS resins are widely used in the fields of electrical and electronic appliances, OA equipment and the like because of their capability of providing a good surface appearance to their moldings, excellent moldability and mechanical properties and the like.
In recent years, there has been a tendency that articles of light-color tone are prepared in OA equipment. Since the light-colored articles have a tendency in which the change of color tone in long-time use manifests easily, the resin materials having good light-resistance have come to be used with increasing popularity. Presently, most of these articles are produced by injection molding. With technical innovations in the art of molding, such as automation of the molding operations by the introduction of a hot-runner system and reduction of the molding time, it has been requested for a molding resin material to satisfy the elevated quality requirements and to be free of defective molding. Particularly, as regards the reduction of molding time, it is remarkable that there is a tendency for the so-called whitening phenomenon take place when the molded article is removed, due to reduced cooling time. Therefore, a resin material having good mold releasability is required.
From the environmental and hygienic standpoint, halogenated epoxy oligomers has been used as a flame-retardant which generates little noxious dioxin when burned. Such halogenated epoxy oligomers can be roughly classified into two types: oligomers having epoxy groups at both terminals of the molecular chain (uncapped type) and oligomers in which the terminal epoxy groups have been subjected to ring-opening addition reaction with tribromophenol (capped type).
The uncapped type flame retardants have high light resistance but are very poor in mold releasability and heat stability. On the other hand, the capped type flame retardants exhibit relatively good mold releasability and heat stability but are intolerably low in light resistance. When these two types of flame retardant are used in combination, the deterioration of the respective flame retardants are manifested in the product.
Thus, the mold releasability and light resistance are the antinomic properties, and there is yet available no flame-retardant resin material that is excellent in both mold releasability and light resistance. Therefore, a flame-retardant resin having both excellent releasability and high light resistance has strongly been required.
As a result of the present inventors' earnest studies on the above problem, it has been found that by blending a specific graft copolymer and a specific flame-retardant in a specified ratio, the obtained resin composition shows excellent mold releasability, heat stability and light resistance. The present invention has been attained on the basis of this finding.